Machinery arrangements for marine vessels conventionally comprise one or more combustion units, such as diesel engines, oil-fired boilers, incinerators, etc. The combustion units usually have independent exhaust gas duct assemblies, whereby also the cleaning of exhaust gases takes place separately for each combustion unit.
Gases coming from oil-fired boilers are sometimes referred to as flue gases. Gases from diesel engines are mostly called exhaust gases. In the following the general term exhaust gas will be used with regard to gases from all relevant types of combustion units.
Reduction of exhaust gas emissions can be obtained by improving the performance of the combustion units, by using cleaner fuel, or by cleaning the exhaust gases.
In previously known solutions, with regard to cleaning the exhaust gases, machinery arrangements have been provided with exhaust gas cleaning systems for nitric oxides (NOx). Presently, however, due to increasing demands to reduce exhaust gas emissions, especially in port conditions and near the coast, there will be a need to clean sulphuric oxides (SOx) emanating from sulphur rich fuels, such as conventional heavy fuel oil.
Generally speaking, exhaust gas cleaning systems cause flow resistance in the exhaust gas duct assembly, which is undesirable in view of the efficiency of the exhaust gas cleaning and the operation of the combustion units.